Excess Oxygen Conditions Research Articles

Effect of (M = Co, Cu, Cr, and Mo) M/CeO2-MgO catalysts in selective catalytic reduction of NOx with hydrogen under excess oxygen condition

Efficient NOx removal is an important for controlling air pollution, and developing effective catalysts is a significant challenge. In this study, (M = Co, Cu, Cr, and Mo) M/CeO2-MgO catalysts were prepared by the co-precipitation method followed by the wet-impregnation method for NO removal by H2-SCR technology. The catalysts were characterized by BET, XRD, XPS, TEM, and H2-TPR. The CeO2-MgO showed the BET surface area of 78 m2/g, which is slightly decreased after the impregnation of Cu, Co, Cr, and Mo metals. X-ray diffraction showed the presence of cubic phase by CeO2 and MgO. The Cu/CeO2-MgO catalyst shows the highest lattice strain, Ce3+ content, and adsorbed oxygen with values of 0.66%, 30.54%, and 74.12%. A maximum NOx conversion of 78% was achieved over the Cu/CeO2-MgO catalyst with a slightly large temperature window (100–250 ℃) among all the catalysts. The catalyst’s sequence of NOx conversion was as follows: Cu/CeO2-MgO > Mo/CeO2-MgO > Co/CeO2-MgO > Cr/CeO2-MgO > CeO2-MgO. The N2 selectivity followed the same order as NO conversion except for the Cr catalyst, which performed better than the Co impregnated catalyst.

Methane Catalytic Combustion under Lean Conditions over Pristine and Ir-Loaded La1-xSrxMnO3 Perovskites: Efficiency, Hysteresis, and Time-on-Stream and Thermal Aging Stabilities.

The increasing use of natural gas as an efficient, reliable, affordable, and cleaner energy source, compared with other fossil fuels, has brought the catalytic CH4 complete oxidation reaction into the spotlight as a simple and economic way to control the amount of unconverted methane escaping into the atmosphere. CH4 emissions are a major contributor to the 'greenhouse effect', and therefore, they need to be effectively reduced. Catalytic CH4 oxidation is a promising method that can be used for this purpose. Detailed studies of the activity, oxidative thermal aging, and the time-on-stream (TOS) stability of pristine La1-xSrxMnO3 perovskites (LSXM; X = % substitution of La with Sr = 0, 30, 50 and 70%) and iridium-loaded Ir/La1-xSrxMnO3 (Ir/LSXM) perovskite catalysts were conducted in a temperature range of 400-970 °C to achieve complete methane oxidation under excess oxygen (lean) conditions. The effect of X on the properties of the perovskites, and thus, their catalytic performance during heating/cooling cycles, was studied using samples that were subjected to various pretreatment conditions in order to gain an in-depth understanding of the structure-activity/stability correlations. Large (up to ca. 300 °C in terms of T50) inverted volcano-type differences in catalytic activity were found as a function of X, with the most active catalysts being those where X = 0%, and the least active were those where X = 50%. Inverse hysteresis phenomena (steady-state rate multiplicities) were revealed in heating/cooling cycles under reaction conditions, the occurrence of which was found to depend strongly on the employed catalyst pre-treatment (pre-reduction or pre-oxidation), while their shape and the loop amplitude were found to depend on X and the presence of Ir. All findings were consistently interpreted, which involved a two-term mechanistic model that utilized the synergy of Eley-Rideal and Mars-van Krevelen kinetics.

Activity and segregation behavior of Pd75%Ag25%(1 1 1) during CO oxidation – An in situ NAP-XPS investigation

The surface reactivity during CO oxidation over Pd(111) and Pd75%Ag25%(111) single crystals has been investigated using near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) under excess oxygen conditions (p ≈ 2 mbar, O2:CO=10). The (√6×√6) Pd5O4 surface oxide is present on Pd(111) when the surface is highly active under the applied conditions. The CO2 formation profile follows a hysteresis upon temperature cycling between 150 and 450 °C that depends on the temperature ramp rate. The behavior is different for Pd75%Ag25%(111), with the CO2 formation rate considerably lower, no surface oxide and only chemisorbed oxygen present at the surface at high temperature, reversible scrambling of the (near) surface Pd/(Pd+Ag) ratio, and no hysteresis behavior observed. The results suggest that the reactant activation is affected by both surface composition and surface termination, i.e. mechanistically different on Pd75%Ag25%(111) than Pd(111), and less efficient on (111) as compared to the (100) alloy counterpart.

Low-temperature NH3-SCR of NO over robust RuNi/Al-SBA-15 catalysts: Effect of Ru loading

Selective catalytic reduction of nitric oxide using ammonia in the presence of excess oxygen remains a major challenge. In the present work, we developed mesoporous Al-SBA-15 supported NiRu catalysts with a high surface area and ordered mesoporous structure. The monometallic Ni catalyst were prepared by the modified beta-cyclodextrin impregnation method by maintaining 1/50 mol of β-CD/Ni and bimetallic NiRu catalyst was prepared by maintaining constant loading of 8 wt% Ni with different wt%. loading of xwt% Ru (x = 2, 4, 6 and 8). The developed catalysts were characterized by XRD, N2 sorption, FT-IR, Py-IR, UV-DRS, HRSEM, HRTEM and XPS. The NH3-SCR efficiency of both monometallic (Ni) and bimetallic (NiRu) catalysts are discussed. Additionally, monometallic 8 wt% Ni and Ru supported catalysts have been also synthesized by the conventional impregnation method for purposes of comparison. The remarkable low-temperature NH3-SCR conversion (90.2% NO conversion at 300 °C) of 8Ru8Ni/Al-SBA-15 catalyst under excess oxygen condition (7%) and superior % promotion (87%) of ruthenium addition was demonstrated with excellent textural properties, stability and corroborated with the physicochemical properties of the catalyst.

Catalysts Optimization of WO3‐SiO2 Supported Iridium for NOx Reduction by CO under Excess Oxygen Conditions

AbstractA series of Ir‐based catalysts were prepared by ultrasonic‐assisted equal‐volume impregnation to evaluate the catalytic performance of selective catalytic reduction of NOx by CO (CO‐SCR) with excess O2 in simulated flue gas. We investigated the effects of different carrier, Ir loading, and composite carrier ratio (W/Si) on the CO‐SCR activities. The results showed that WO3 and SiO2 were effective carriers for the CO‐SCR reaction under oxygen‐rich conditions. Results of XRD and H2‐TPR studies indicated that metal Ir strongly interacted with carrier WO3 and SiO2, respectively, which improved the surface dispersion of active component Ir species and was conducive to the removal of NOx and CO. When W/Si molar ratio was 1/9 and Ir loading was 2 wt%, the Ir/WO3‐SiO2 catalyst reached 49 % NOx conversion and 76 % CO conversion at 225°C, while NO2 yield was also only 5 ppm. The effects of O2, SO2, and H2O on the structure of Ir/WO3‐SiO2 were analyzed by XRD and XPS characterization methods. It was found that O2 could oxidize Ir species to IrO2, thereby inhibiting NOx reduction. A low concentration of SO2 can weaken the process of Ir oxidation, promote NOx reduction, and improve catalytic activity. H2O can reduce the NOx conversion rate and inhibit the CO‐SCR reaction, but the inhibition effect is reversible.

Complete nitrogen removal from over-aeration treated black-odorous water via adding aerobic denitrifiers and iron-carbon micro-electrolysis carriers

Over-aeration is usually unavoidable for removing ammonia nitrogen from black-odorous water bodies, which consumes a large amount of organic matter and creates a long-term oxygen-rich environment, limiting the denitrification process in the water. This study aims to investigate the synergistic effect of aerobic denitrifying bacteria and iron-carbon micro-electrolysis (IC-ME) carriers on complete nitrogen removal from the over-aerated black-odorous water. For nitrification, aeration can completely oxidize ammonia nitrogen to nitrate. For denitrification, adding aerobic denitrifying bacteria Pseudomonas ATCC 9027 allowed the nitrate reduction to occur under conditions of excess oxygen and enriched indigenous denitrifying bacteria (1.45% increase in cumulative abundance). These changes brought by Pseudomonas ATCC 9027 reduced the total nitrogen concentration from 12.07 to 7.12 mg/L. Besides, research has shown that IC-ME carriers as electron donors can provide additional electrons and improve the electron transport system activity by 0.07 μg O2/(g protein∙min) in the denitrification process. Enzyme activity test and metagenome analysis revealed that enzymes and genes associated with denitrification were both upregulated with the addition of Pseudomonas ATCC 9027 and IC-ME carriers. Specifically, the improvement for activities of nitrate reductase (NAR), nitrite reductase (NIR), nitric oxide reductase (NOR), nitrous oxide reductase (NOS), and cumulative abundance of denitrification genes was 0.93 μmol NO2−-N/(g·d), 3.74 μmol NO2−-N/(g·d), 0.18 μmol N2O-N/(g·d) and 0.09 μmol N2O-N/(g·d) and 1.48%, respectively. These findings provide an understanding of the cooperative mechanism of aerobic denitrifying bacteria and IC-ME carriers in enhancing nitrogen removal from over-aerated black-odorous water bodies.

Modelling Cell Growth and Polyhydroxyalkanoate (PHA) Polymer Synthesis by Pseudomonas Putida LS46 under Oxygen-Limiting Conditions

Background: Polyhydroxyalkanoates (PHAs) are biodegradable, biocompatible, and non-toxic polymers synthesized by bacteria that may be used to displace some petroleum-based plastic materials. One of the major barriers to the commercialization of PHA biosynthesis is the high cost of production. Objective: Oxygen-limitation is known to greatly influence bacterial cell growth and PHA production. In this study, the growth and synthesis of medium chain length PHAs (mcl-PHAs) by Pseudomonas putida LS46, cultured in batch-mode with octanoic acid, under oxygen-limited conditions, was modeled. Methods: Four models, including the Monod model, incorporated Leudeking-Piret (MLP), the Moser model incorporated Leudeking-Piret (Moser-LP), the Logistic model incorporated Leudeking- Piret (LLP), and the Modified Logistic model incorporated Leudeking-Piret (MLLP) were investigated. Kinetic parameters of each model were calibrated using the multi-objective optimization algorithm, Pareto Archived Dynamically Dimensioned Search (PA-DDS), by minimizing the sum of absolute error (SAE) for PHA production and growth simultaneously. Results and Conclusions: Among the four models, MLP and Moser-LP models adequately represented the experimental data for oxygen-limited conditions. However, the MLP and Moser-LP models could not adequately simulate PHA production under oxygen-excess conditions. Modeling cell growth and PHA will assist in the development of a strategy for industrial-scale production.

Interaction of NH3 and NO under combustion conditions. Experimental flow reactor study and kinetic modeling simulation

The interaction between ammonia and NO under combustion conditions is analyzed in the present work, from both experimental and kinetic modelling points of view. An experimental systematic study of the influence of the main variables for the NH3NO interaction is made using a laboratory tubular flow reactor installation. Experiments are performed at atmospheric pressure and variables analyzed include: temperature in the 700–1500 K range, air stoichiometry, from pyrolysis to very oxidizing conditions, and the NH3/NO ratio, in the 0.7–3.5 range. Nitrogen and argon have been used as diluent gas. A literature reaction mechanism has been used to simulate the present experimental results and discuss the main findings. Reaction path analysis has allowed the identification of the reaction routes under the studied conditions. The simulations reflect the main experimental trends observed. Main results show that NO reduction by NH3 occurs at any conditions studied, but is more intense under oxygen excess conditions. Interactions of NH3 and NO proceeds in a molar basis with optimum conversions of NO of up to almost 100%.

Reaction Mechanism of H2-Assisted C3H6-SCR over Ag-CexZr Catalyst as Investigated by In situ FTIR

A series of silver-doped cerium zirconium oxide(Ag-CexZr) samples was synthesized successfully for selective catalytic reduction of nitric oxide(NO) with hydrogen and propene(H2/C3H6-SCR) under excess oxygen condition. The catalytic activity test proved that Ag-Ce0.4Zr exhibited the best C3H6-SCR activity. Hydrogen(H2) significantly enhanced NO conversion and widened the temperature window. Multi-technology characterizations were conducted to ascertain the properties of fabricated catalysts including X-ray diffraction(XRD), Fourier transform infrared spectrometry(FTIR), scanning electron microscopy(SEM) and H2 temperature programmed reduction (H2-TPR). In situ FTIR results demonstrated that various types of nitrates and chelating nitrite were generated on Ag-CexZr after introduction of NO. Besides, adding H2 could increase the concentration of bidentate nitrate and chelated bidentate nitrate dramatically, especially for Ag-Ce0.4Zr catalyst. Transient reaction between pre-adsorbing NO and C3H6/C3H6+H2 illuminated that the most active intermediate was chelating nitrite,which was promoted significantly by H2 participation. Furthermore, adding H2 improved the formation of organo-nitro(R-NO2), which was the key intermediate in C3H6-SCR. The reaction mechanism over Ag-CexZr catalysts was proposed at 200 °C as follows: nitric oxide(NO)+propene(C3H6)+hydrogen(H2)+oxygen(O2)→chelating nitrite(NO2−)+acrylate-type species(CxHyOz)→organo-nitro(R-NO2)→isocyanate(—NCO)+cyanide(—CN)→nitrogen(N2).

Effects of manganese content and calcination temperature on Mn/Zr-PILM catalyst for low-temperature selective catalytic reduction of NOx by NH3 in metallurgical sintering flue gas.

The effects of manganese content, carrier calcination temperature, and catalyst calcination temperature of manganese-based zirconium pillared intercalated montmorillonite (Mn/Zr-PILM) catalysts were investigated for low-temperature selective catalytic reduction of NOx by NH3 (NH3-SCR) in the metallurgical sintering flue gas. The physicochemical properties of these catalysts can be characterized by X-ray diffraction (XRD), N2 adsorption-desorption isotherm, and temperature-programmed desorption of ammonia (NH3-TPD). The 10Mn/Zr400-PILM(300) catalyst had the highest NOx conversion under excess oxygen conditions (15vol% oxygen) and reached 91.8% NOx conversion at 200°C. It was found that when the loading of manganese was 10wt.%, the catalyst had the highest catalytic activity and the manganese-active component was highly dispersed on the Zr-PILM surface. The optimal calcination temperature of the Zr-PILM was 400°C because the catalyst pore size was concentrated at 1.92nm and the catalyst had the most acidic sites. And the optimum calcination temperature of the catalyst was 300°C. This was because excessive calcination temperature promoted the manganese oxide polymerization and reduced the catalytic activity of the catalyst.

Individual stages of bacterial dichloromethane degradation mapped by carbon and chlorine stable isotope analysis

The fractionation of carbon and chlorine stable isotopes of dichloromethane (CH2Cl2, DCM) upon dechlorination by cells of the aerobic methylotroph Methylobacterium extorquens DM4 and by purified DCM dehalogenases of the glutathione S-transferase family was analyzed. Isotope effects for individual steps of the multi-stage DCM degradation process, including transfer across the cell wall from the aqueous medium to the cell cytoplasm, dehalogenase binding, and catalytic reaction, were considered. The observed carbon and chlorine isotope fractionation accompanying DCM consumption by cell supensions and enzymes was mainly determined by the breaking of CCl bonds, and not by inflow of DCM into cells. Chlorine isotope effects of DCM dehalogenation were initially masked in high density cultures, presumably due to inverse isotope effects of non-specific DCM oxidation under conditions of oxygen excess. Glutathione cofactor supply remarkably affected the correlation of variations of DCM carbon and chlorine stable isotopes (Δδ13C/Δδ37Cl), increasing corresponding ratio from 7.2–8.6 to 9.6–10.5 under conditions of glutathione deficiency. This suggests that enzymatic reaction of DCM with glutathione thiolate may involve stepwise breaking and making of bonds with the carbon atom of DCM, unlike the uncatalyzed reaction, which is a one-stage process, as shown by quantum-chemical modeling.

Manganese-based catalyst for NO removal at low temperatures: thermodynamics analysis and experimental validation

Selective catalytic reduction of nitrogen oxides with loaded urea is a novel method for removing NO under excess oxygen and low temperature conditions. In present work, a comprehensive thermodynamic study for NO removal is executed based on the Gibbs free energy change. This research mainly includes the detailed analyses of NO removal mechanism, the feasibility analyses for manganese as the active element and the experimental study for synthesized manganese-based catalyst (preparation, characterization and performance test). The catalyst in present study can reach 82% NO conversion and near 98% N2 selectivity at 50 °C, which validates the correctness of the thermodynamic calculations.

Studies on H2 assisted LPG reduction of NO over Ag/Al2O3 catalyst

Hydrocarbon-Selective catalytic reduction (HC-SCR) is a potential method to remove NOx under excess oxygen conditions such as diesel engine exhausts and lean burn engines. Ag-Al 2 O 3 is a good catalyst for HC-SCR of NOx under lean-burn conditions. Further, addition of H 2 is effective for enhancing HC-SCR activity. This effect is unique to silver and to specific Ag/support combinations, namely, Ag/ δ- Al 2 O 3 .Therefore, in the present investigation, Ag/Al 2 O 3 catalyst containing 2.0 wt.% Ag was prepared by wet-impregnation method. The catalysts were characterized by various techniques like low temperature N 2 adsorption, XRD, XPS and SEM. Two different reductants CO and LPG were comparatively studied for SCR of NO over the Ag-Al 2 O 3 catalyst without and with H 2 -assisted. The experiments were performed in a fixed bed tubular down flow reactor under the following conditions: composition of gas mixture was 0.13% NO, 2.50% LPG/CO, 1% H 2 , 10% O 2, rest Ar; total flow rate of 60 ml/min, temperature varied from 50-400 o C and pressure 1 atm. High conversion of NO, around 100%, is achieved using LPG as a reductant with H 2 and without H 2 . Results showed that light off temperature of catalyst significantly reduced by the introduction of H 2 in feed stream with LPG reductant. The maximum conversions of NO with CO and LPG reductants were 35.15 and 97.79 % at 224 and 365 o C respectively. While, the maximum conversions with H 2 -LPG and H 2 -CO reductants were 100 and 99.46% at 117 and 220 o C respectively. Therefore, H 2 -LPG-SCR system can be used to get 100% NO reduction at low temperature. Very few studies are dedicated to LPG as reductant.

Biogeochemical oxidation of calcium sulfite hemihydrate to gypsum in flue gas desulfurization byproduct using sulfur-oxidizing bacteria

Flue gas desulfurization (FGD) is a well-established air treatment technology for coal and oil combustion gases that commonly uses lime or pulverized limestone aqueous slurries to precipitate sulfur dioxide (SO2) as crystalline calcium salts. Under forced oxidation (excess oxygen) conditions, FGD byproduct contains almost entirely (>92%) gypsum (CaSO4·2H2O), a useful and marketable commodity. In contrast, FGD byproduct formed in oxygen deficient oxidation systems contains a high percentage of hannebachite (CaSO3·0.5H2O) to yield a material with no commercial value, poor dewatering characteristics, and that is typically disposed in landfills. Hannebachite in FGD byproduct can be chemically converted to gypsum; however, the conditions that support rapid formation of gypsum require large quantities of acids or oxidizers. This work describes a novel, patent pending application of microbial physiology where a natural consortium of sulfur-oxidizing bacteria (SOB) was used to convert hannebachite-enriched FGD byproduct into a commercially valuable, gypsum-enriched product (US Patent Assignment 503373611). To optimize the conversion of hannebachite into gypsum, physiological studies on the SOB were performed to define their growth characteristics. The SOB were found to be aerobic, mesophilic, neutrophilic, and dependent on a ready supply of ammonia. They were capable of converting hannebachite to gypsum at a rate of approximately five percent per day when the culture was applied to a 20 percent FGD byproduct slurry and SOB growth medium. 16S rDNA sequencing revealed that the SOB consortium contained a variety of different bacterial genera including both SOB and sulfate-reducing bacteria. Halothiobacillus, Thiovirga and Thiomonas were the dominant sulfur-oxidizing genera.

Selective reduction of NOx by C3H6 over Pd–NiO/(Y0.99Ba0.01)2O3 under oxygen excess conditions

A Pd-NiO/Y(Ba)2O3 developed catalyst shows high activity to selective NOx reduction into N2 (yield ~70%) with C3H6 under oxygen excess conditions. Y(Ba)2O3 support material is active to NO direct decomposition at high temperatures and is considered to selectively adsorb NO. By depositing NiO and Pd simultaneously, high NO selective reduction activity is exhibited around 200°C and the activity is hardly affected by the addition of water in the feed stream.

Near Ambient Pressure XPS Investigation of CO Oxidation Over Pd3Au(100)

The CO oxidation behavior under excess oxygen and near stoichiometric conditions over the surface of Pd3Au(100) has been studied by combining near-ambient pressure X-ray photoelectron spectroscopy and quadrupole mass spectrometry and compared to Pd(100). During heating and cooling cycles, normal hysteresis in the CO2 production, i.e. with the light-off temperature being higher than the extinction temperature, is observed for both surfaces. On both Pd3Au(100) and Pd(100) the (√5 × √5)R27° surface oxide structure is present during CO2 production under excess oxygen conditions (O2:CO = 10:1), while at near stoichiometric conditions (O2:CO = 1:1) the surfaces are covered with atomic oxygen. Au as alloying element hence induces only minor differences in the observed hysteresis and the active phase compared to pure Pd. Alloying with Au thus yields a different behavior compared to Ag, where reversed hysteresis is observed for CO2 production over Pd75Ag25(100) at similar conditions [Fernandes et al., ACS Catal. (2016) 4154].

Ce-Based Catalysts for the Selective Catalytic Reduction of NOx in the Presence of Excess Oxygen and Simulated Diesel Engine Exhaust Conditions

A family of various cerium oxide-based catalysts were synthesized by adopting flame aerosol (FSP), coprecipitation, wet impregnation, and hydrothermal synthesis techniques. The resulting catalysts were explored for the selective catalytic reduction (SCR) of NOx using NH3 as reductant. In our studies, both the preparation method and the Ce/W ratios were found to be critical variables for successful catalyst promotion. For the industrial realization, we have scaled up the SCR activity tests. The microreactor catalytic formulations at simulated diesel engine exhaust conditions revealed that the Ce–W (1:1 atomic ratio) and Ce–W/TiO2 catalysts showed high deNOx activity, while the other catalysts’ activity was found to be rather low. Of interest is the finding that the Ce–W/TiO2/cordierite and Ce–W (1:1 atomic ratio)/cordierite formulations show impressive deNOx performance and high N2 selectivity with respect to a commercial vanadia based reference currently used for mobile applications. To gain fundamental i...

Microwave Irradiation Coupled with MeOx/Al2O3 (Me=Cu, Mn, Ce) Catalysts for Nitrogen Monoxide Removal from Flue Gas at Low Temperatures

AbstractThe direct catalytic decomposition of nitrogen monoxide (NO) into nitrogen (N2) and oxygen (O2) with high efficiency remains a significant challenge at low temperatures under excess oxygen conditions. Herein, we report the direct decomposition of NO by microwave‐assisted catalysis over metal oxide catalysts MeOx/Al2O3 (Me=Cu, Mn, Ce) for the first time under these conditions. The CeCuMnOx/Al2O3 catalyst displays an impressively high efficiency with a high NO conversion and N2 selectivity, reaching up to 94.8 % and 98.7 %, respectively, even at a low temperature of 250 °C and oxygen excess of 10 %. Moreover, the cerium‐doped MeOx/Al2O3 (Me=Cu, Mn) catalysts enhance the catalytic performance dramatically, and CeCuMnOx/Al2O3 is more active than CeCuOx/Al2O3 and CeMnOx/Al2O3 under microwave irradiation. Comparatively, these catalysts show extremely low catalytic activity under conventional reaction conditions. Furthermore, the catalytic performance of NO decomposition under microwave irradiation is hardly influenced by the oxygen concentration.

Effect of Alkali Promoters (K) on Nitrous Oxide Abatement Over Ir/Al2O3 Catalysts

The promoting impact of potassium (0–1 wt% K) on nitrous oxide (N2O) catalytic decomposition over Ir/Al2O3 is investigated under both oxygen deficient and oxygen excess conditions. All samples were characterized by means of X-ray powder diffraction (XRD), temperature-programmed reduction (H2-TPR), ammonia desorption (NH3-TPD) and Fourier Transform Infrared Spectroscopy of pyridine adsorption (FTIR-Pyridine). The results reveal that the K-free Ir/Al2O3 catalyst consists mainly of the IrO2 phase, exhibiting also significant Lewis acidity, which is gradually eliminated by the addition of K. Catalytic performance results showed that the deN2O performance in the absence of O2 in the feed mixture is negatively affected upon increasing potassium loading. However, under oxygen excess conditions, a pronounced effect of K is observed. Although the catalytic performance of the un-doped catalyst is drastically hindered by the presence of O2, the K-promotion notably prohibits the oxygen poisoning. The optimum deN2O performance under oxygen excess conditions is obtained with potassium loading of 0.5 wt% K, which offers complete conversion of N2O at 580 °C, instead of the corresponding 50 % N2O conversion achieved with the un-modified sample. On the basis of characterization results, it was concluded that alkali-doping in combination with oxygen excess conditions are required towards the formation of active Ir entities.

Unsteady-state operation of supported platinum catalysts for high conversion of methane

Total oxidation of methane over model monolith catalysts with platinum supported on alumina, alumina–ceria and ceria has been studied under unsteady-state operation of the feed gas stoichiometry. The general activity for methane oxidation follows the order Pt/alumina<Pt/alumina–ceria<Pt/ceria. Thanks to high catalytic activity at the gas composition switches, increased cycling frequency between oxygen excess and oxygen free conditions increases the average methane conversion significantly from 11% to 58% for Pt/alumina and from 25% to 87% for Pt/alumina–ceria. The corresponding stationary methane conversion is 10% and 19%, respectively. The underlying reason for the enhanced catalytic activity is likely twofold namely that periods with detrimentally high coverage of either oxygen or carbon are shortened and that the transients induce a highly active (chemical) state of the catalyst, thus, facilitating high average conversion of methane.